This invention relates generally to manipulating fluid flow over a surface. More specifically, this invention relates to both actively and passively manipulating ducted fluid flow over an aerodynamic or hydrodynamic surface. The fluid flow over the ducted surface is manipulated by very-small-scale effectors at the surface, wherein these very-small-scale effectors achieve a desired fluid flow behavior over the surface.
One of the most commonly used methods to control local boundary layer separation within ducted systems is the placement of vortex generators upstream of the layer separation within a natural fluid flow. Vortex generators are small wing like sections mounted on the inside surface of the ducted fluid flow and inclined at an angle to the fluid flow to generate a shed vortex. The height chosen for the best interaction between the boundary layer and the vortex generator is usually the boundary layer thickness. The principle of boundary layer control by vortex generation relies on induced mixing between the primary fluid flow and the secondary fluid flow. The mixing is promoted by vortices trailing longitudinally near the edge of the boundary layer. Fluid particles with high momentum in the stream direction are swept along helical paths toward the duct surface to mix with and, to some extent replace low momentum boundary layer flow. This is a continuous process that provides a source to counter the natural growth of the boundary layer creating adverse pressure gradients and low energy secondary flow accumulation.
The use of vortex generators in curved ducts to reduce distortion and improve total pressure recovery has been applied routinely. Many investigations have been made in which small-geometry surface configurations effect turbulent flow at the boundary layers. Particular attention has been paid to the provision of surfaces in which an array of small longitudinal elements extend over the turbulent boundary layer region of a surface in the direction of fluid flow over the surface, to reduce momentum transport or drag. Some experimental results indicate that net surface drag reductions of up to about 7% can be achieved. However, these structures, used to induce vortices, are fixed and address vortex generation with a fluid flow. It would be desirable to provide a mechanism to actively manipulate the vortex generation within a dynamic fluid flow condition.
As computers increasingly leave fixed locations and are used in direct physical applications, new opportunities are perceived for applying these powerful computational devices to solve real world problems in real time. To exploit these opportunities systems are needed which can sense and act. Micro-fabricated Electro-Mechanical Systems (MEMS) are perfectly suited to exploit and solve these real world problems.
MEMS offer the integration of micro-machined mechanical devices and microelectronics. Mechanical components in MEMS, like transistors in micro-electronics, have dimensions that are measured in microns. These electro-mechanical devices may include discrete effectors and sensors. More than anything else, MEMS is a fabrication approach that conveys the advantages of miniaturization, multiple components and microelectronics to the design and construction of integrated electro-mechanical systems.
To utilize an individual MEMS device to control or manipulate microscopic conditions can be useful. However, it would be desirable to achieve macroscopic effects by manipulating microscopic conditions. These microscopic effects can be achieved by the MEMS passively or by actively manipulating these devices. Furthermore, in a system utilizing active manipulation, it may be desirable to utilize a sophisticated control system in conjunction with a large array of MEMS devices to control and manipulate such macroscopic effects.
The present invention provides a system and method for manipulating and controlling aerodynamic or hydrodynamic fluid flow over a surface that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods used of fluid flow control.
More specifically, the present invention provides a system and method to control aerodynamic or hydrodynamic fluid flow behavior of fluid flow using very-small-scale effectors. The system and method for manipulating and controlling fluid flow over a surface includes the placement of arrays of very-small-scale effectors on ducted surfaces bounding the ducted fluid flow. In one embodiment, these effectors may passively manipulate the ducted fluid flow.
In a second embodiment, these very-small-scale effectors are actively manipulated to control the flow behavior of the fluid flow and prevent natural flow separation within the primary fluid flow.
An additional embodiment of the present invention includes the use of MEMS devices as the very-small-scale effectors. In this case the very-small-scale effectors are smaller than a duct boundary layer thickness of a ducted fluid flow. Furthermore these very-small-scale effectors may be dimensioned at an order of one-tenth of the boundary layer thickness.
A third embodiment of the present invention further senses the flow conditions within in the primary and secondary fluid flow, with a flow sensor system. This relieves computational burdens imposed by prior art systems which failed to sense actual conditions and relied on computationally intensive mathematical models to determine the fluid flow conditions. Further, this eliminates the inaccuracies associated with such mathematical models and provides real time actual feedback. A control system is employed to actively direct the array of very-small-scale effectors in response to the sensed flow conditions to produce a desired fluid flow within the ducted fluid flow.
Manipulating boundary layer conditions for a ducted fluid flow expands the possible geometries available for ducting systems used to contain such a fluid flow. This is highly desirable where exotic geometries are required. One example of such use may be in a low-observable tactical aircraft. However, the present invention need not be limited to tactical aircraft as low-observable technology has many applications as known to those skilled in the art.
Manipulating a ducted fluid flow can result in reduced fatigue and cyclical stress effects on downstream components located within the fluid flow, such as an aircraft engine or turbine, as the adverse pressure gradients within the duct can be minimized or eliminated. Included in the present invention is the possibility of using effectors that are actively controlled either as pulsating effectors that are either on or off (non-pulsating) or are actively controlled through a system that uses small sensors (like MEMS) to control the effectors.
The operational performance of components, such as an aircraft engine or turbine, located within the ducted fluid flow can be enhanced by actively monitoring and controlling the fluid flow behavior to prevent operational failures such as engine stalling induced by fluid flow through the engine.
The present invention provides an important technical advantage by allowing a dynamic primary fluid flow to be manipulated by an array of very-small-scale effectors to achieve a greater pressure recovery of the primary fluid flow.
The use of vortex generators in curved ducts to reduce distortion and improve total pressure recovery has been applied routinely. Recent investigations have shown that a xe2x80x9cglobalxe2x80x9d approach to the application of conventional size vortex generators or vortex generator jets works better than the older approach which was specifically aimed at the prevention of boundary layer flow separation. The present invention applies to the use of very-small-scale devices (effectors) to accomplish this xe2x80x9cglobalxe2x80x9d approach to flow control. The present invention provides another technical advantage by preventing or limiting natural flow separation within a ducted fluid flow. This is achieved by manipulating an array of very-small-scale effectors according to conditions sensed within the fluid flow to achieve a macroscopic effect. Individually, these very-small-scale effectors induce vortex generation at the boundary layer. These vortices induce mixing between the primary fluid flow and the secondary fluid flow. The mixing is promoted by vortices trailing longitudinally near the edge of the boundary layer. Fluid particles with high momentum in the stream direction are swept along helical paths toward the duct surface to mix with and, to some extent replace low momentum boundary layer flow. By manipulating the vortex generation across an array of very-small-scale effectors, a macro-scale influence can be achieved. This provides a macro-scale source to counter the natural growth of the boundary layer, thereby eliminating and low energy secondary flow accumulation within the primary fluid flow. In an additional embodiment, since the induction of these vortices can be actively controlled, it is possible for the present invention to respond to changing conditions effecting the dynamic fluid flow.
Moreover, the present invention provides yet another technical advantage by allowing a greater flexibility in the design of a ducting system to be associated with the primary fluid flow. This flexibility allows both inlet and exhaust ducting to take exotic or serpentine shapes as is often required by other engineering design constraints, such as those imposed in the design of a low-observable tactical aircraft.
Yet another technical advantage provided by the present invention, when applied to a low-observable tactical aircraft, is the increased design flexibility in providing ducting systems optimized to minimize radar reflections, disperse exhaust signatures, and provide adequate airflow to the components located within the ducted fluid flow of a low-observable tactical aircraft.